Image forming apparatus

ABSTRACT

The present invention has been made to provide an image forming apparatus capable of suppressing occurrence of a problem which is based on a sheet feeding speed with a simple configuration without increasing cost and changing a process speed.  
     The image forming apparatus according to the present invention comprises: a drive controller  101  that controls the drive speed of an intermediate feeding roller  38  for feeding a sheet to a regist roller  37  for performing skew correction for the sheet; and a feeding speed information acquisition section  102  that acquires information relating the feeding speed of the sheet to be fed to the intermediate feeding roller  38.  The drive controller  101  controls the drive of the intermediate feeding roller  38  with a feeding speed for duplex printing and a process speed based on the information relating to the feeding speed acquired by the feeding speed information acquisition section  102.  The feeding speed for duplex printing is a speed at which a sheet to be resupplied to the intermediate feeding roller  38  for image forming onto the second surface thereof is received by the intermediate feeding roller  38  after the sheet has been passed through the regist roller  37  and a toner image has been formed onto the first surface thereof. The process speed is a speed at which a sheet is fed by both the intermediate feeding roller  38  and regist roller  37.  The drive of intermediate feeding roller  38  is controlled such that the feeding speed for duplex printing becomes 1 to 1.3 times the process speed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus that forms an image on a sheet to be supplied and, more particularly, to control of a sheet feeding speed.

2. Description of the Related Art

In an image forming apparatus, an intermediate feeding roller that feeds a sheet to a regist roller (roller that performs skew correction or timing adjustment for a sheet being fed) has roles of performing sheet feeding operation at the time when an image is formed onto the sheet in cooperation with the regist roller and receiving a sheet supplied from a sheet supply cassette or sheet, onto the first surface of which an image has already been formed, fed for image forming on the second surface thereof (fed for duplex printing).

It is preferable that the sheet feeding speed of the intermediate feeding roller having the above roles be synchronized with the sheet feeding speed of a feeding roller or regist roller which is a partner for the sheet feeding operation. The sheet feeding speed with which the intermediate feeding roller should be synchronized includes a sheet supply speed (speed at which a sheet supplied from the cassette is fed to the regist roller), a process speed (sheet feeding speed at the time of toner image transfer), and an ADU speed (feeding speed of a sheet to be resupplied for image forming onto the second surface thereof).

In order to improve productivity at the time of duplex printing, a method that uses a pulse motor a lot to increase the process speed or drive the feeding roller for feeding a sheet in an ADU (Automatic Duplexing Unit) has been adopted in the above conventional image forming apparatus (refer to Jpn. Pat. Appln. Laid-Open Publication No. 2001-130811).

In some conventional image forming apparatus, the sheet supply speed, process speed, and ADU speed are set to the same value for the purpose of reducing cost and simplifying a control system. In this case, however, printing efficiency at the time of duplex printing may decrease.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problem, and an object thereof is to provide an image forming apparatus capable of suppressing occurrence of a problem which is based on a sheet feeding speed without changing the process speed.

To solve the above problem, according to a first aspect of the present invention, there is provided an image forming apparatus comprising: a drive controller that controls the drive speed of an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; and a feeding speed information acquisition section that acquires information relating the feeding speed of the sheet to be fed to the intermediate feeding roller, wherein the drive controller controls the drive of the intermediate feeding roller with a feeding speed for duplex printing and a process speed based on the information relating to the feeding speed acquired by the feeding speed information acquisition section, the feeding speed for duplex printing being a speed at which a sheet, which is to be resupplied to the intermediate feeding roller for image forming onto the second surface thereof after it has been passed through the regist roller and a toner image has been formed onto the first surface thereof, is received by the intermediate feeding roller, and the process speed being a speed at which a sheet is fed by both the intermediate feeding roller and regist roller, and the drive controller controls the drive of the intermediate feeding roller such that the feeding speed for duplex printing becomes 1 to 1.3 times the process speed.

According to a second aspect of the present invention, there is provided an image forming apparatus comprising: a drive controller that controls the drive speed of an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; and a feeding speed information acquisition section that acquires information relating the feeding speed of the sheet to be fed to the intermediate feeding roller, wherein the drive controller controls the drive of the intermediate feeding roller with a feeding speed for sheet supply and a process speed, the feeding speed for sheet supply being a speed at which a sheet to be newly supplied to the intermediate feeding roller is received by the intermediate feeding roller, and the process speed being a speed at which a sheet is fed by both the intermediate feeding roller and regist roller, and the drive controller controls the drive of the intermediate feeding roller such that the feeding speed for sheet supply becomes 1 to 1.3 times the process speed.

According to a third aspect of the present invention, there is provided an image forming apparatus comprising: a sheet supply unit that feeds a sheet that has been picked up from a sheet housing section along a sheet feeding path at a first feeding speed; a process speed feeder that feeds the sheet that has been fed to a process section by the sheet supply unit at a second feeding speed lower than the first feeding speed; and an automatic duplexing unit feeder that feeds the sheet that has been fed to an automatic duplexing unit by the process speed feeder at a third feeding speed lower than the second feeding speed, wherein the sheet that has been fed by the automatic duplexing unit feeder is fed again to the process section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the entire configuration of an image forming apparatus according to an embodiment of the present invention;

FIG. 2 is a view for explaining a sheet feeding operation at the portion in front of a regist roller and shows the area surrounded by the dotted line in FIG. 1 in an enlarged manner;

FIG. 3 is a block diagram for explaining the functional configuration of the image forming apparatus according to the embodiment;

FIG. 4 is a timing chart showing sheet feeding timing at the time when duplex printing is performed for A4 size sheet and A3 size sheet;

FIG. 5 is a view for explaining a sheet feeding path in the image forming apparatus according to the embodiment; and

FIG. 6 is a timing chart showing drive timing of a regist roller 37, intermediate feeding roller 38, and feeding rollers other than the intermediate feeding roller 38 in the image forming apparatus according to the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing the entire configuration of an image forming apparatus according to an embodiment of the present invention.

An image forming apparatus according to the embodiment of the present invention includes: cassettes 31, 32, 33, 34 which are sheet housing sections in which sheets are stacked; pick-up rollers 31 b, 32 b, 33 b, 34 b for picking up the sheets; sheet supply rollers 31 a, 32 a, 33 a, 34 a and separating rollers 31 c, 32 c, 33 c, 34 c for feeding the sheets while separating them one by one; a sheet feeding path 35; feeding rollers 36 a to 36 d (motive energy for which is transferred by a clutch) for feeding the sheet from the sheet feeding path 35 to an intermediate feeding roller 38 serving as a sheet supply unit; an ADU (Automatic Duplexing Unit) 5; feeding rollers 5 a to 5 d (motive energy for which is transferred by a clutch) each serving as an automatic duplexing unit feeder for feeding the sheet in the ADU 5; an intermediate feeding roller 38 driven by a pulse motor; a regist roller 37 for performing skew correction and timing adjustment for the sheet (corresponding to process speed feeder); a process section including a photoconductor drum 20 that forms a toner image onto the sheet; a fixing section 24 that fixes the formed toner image to the sheet; a reverse feeding path 28 to which the sheet onto which the toner image has been fixed is guided; reverse rollers 29, 30 for feeding the sheet that has been introduced in the reverse feeding path 28 in a switchback manner; a CPU 108; and a memory 109.

The following processing is performed in the image forming apparatus shown in FIG. 1. Firstly, paper sheets stacked in cassettes 31, 32, 33, or 34 are sequentially picked up by the pick-up rollers 31 b, 32 b, 33 b, or 34 b. The picked up paper sheets are fed to the sheet feeding path 35 while being separated one by one by supply rollers 31 a, 32 a, 33 a, or 34 a and separating rollers 31 c, 32 c, 33 c, or 34 c. The paper sheet that has been fed to the sheet feeding path 35 is then fed to the portion in front of the intermediate feeding roller 38 by feeding rollers 36 a, 36 b, 36 c, or 36 d. The intermediate feeding roller 38 has a role of guiding the sheet that has been fed along the sheet feeding path 35 or sheet that has been fed by the ADU 5 (to be described later) to the regist roller 37 that performs skew correction or timing adjustment for the sheet.

The sheet that has been guided to the regist roller 37 through the intermediate feeding roller 38 is subjected to the skew correction or timing adjustment. After that, a toner image formed on the photoconductor surface of the photoconductor drum 20 is transferred onto the sheet. The toner image that has been transferred onto the sheet is fixed to the sheet in the fixing section 24. In the case of one-side printing, the sheet onto which the toner image has been fixed is directly discharged outside the apparatus. In the case where the duplex printing is performed or one-side printed sheet is reversed before being discharged outside, the sheet is guided to the reverse feeding path 28.

In the case of the duplex printing, the sheet that has been guided to the reverse feeding path 28 is fed to the ADU 5 in a switchback manner by reverse rollers 29 and 30. The sheet that has been fed to the ADU 5 is then fed to the intermediate feeding roller 38 again by feeding rollers 5 a to 5 d. After that, image forming processing is performed for the other surface of the sheet that has been fed through the ADU 5 by the photoconductor drum 20 and fixing section 24. Thus, the duplex printing for the sheet has been completed.

FIG. 2 is a view for explaining a sheet feeding operation at the portion in front of a regist roller and shows the area surrounded by the dotted line in FIG. 1 in an enlarged manner.

As shown in FIG. 2, in the image forming apparatus having the above configuration, in the case where image forming processing is sequentially performed for a plurality of sheets (in the case where a plurality of sheets are sequentially fed to the regist roller 37), a succeeding sheet P2 is temporarily put on standby at a predetermined position S in front of the intermediate feeding roller 38 until aligning of a preceding sheet P1 has been completed by the regist roller. Similarly, a sheet to be fed through the ADU 5 to the regist roller again is temporarily put on standby at a predetermined position S_(A) in the ADU 5 in front of the intermediate feeding roller 38.

FIG. 3 is a block diagram for explaining the functional configuration of the image forming apparatus according to the embodiment. The image forming apparatus according to the present embodiment has a drive controller 101 and a feeding speed information acquisition section 102 in addition to the configuration shown in FIGS. 1 and 2.

The drive controller 101 has a role of controlling the drive speed of the intermediate feeding roller 38 for feeding a sheet to the regist roller 37 for performing skew correction for the sheet to be fed.

The feeding speed information acquisition section 102 has a role of acquiring information (information indicating which path the sheet is fed through) relating to the feeding speed of a sheet to be fed to the intermediate feeding roller 38 based on a detection signal of a sheet detection sensor disposed in the apparatus or a control signal of the CPU 108.

The CPU 108 has a role of performing various processing in the image forming apparatus and another role of executing a program stored in the memory 109 to realize various functions. The memory 109 is constituted by, for example, a ROM or RAM and has a role of storing various information and programs utilized in the image forming apparatus.

Based on the information relating to the feeding speed acquired by the feeding speed information acquisition section 102, the drive controller 101 controls the drive of the intermediate feeding roller 38 with a feeding speed for duplex printing and a process speed. The feeding speed for duplex printing is a speed at which a sheet, which is to be resupplied to the intermediate feeding roller 38 for image forming onto the second surface thereof after it has been passed through the regist roller 37 and a toner image has been formed onto the first surface thereof, is received by the intermediate feeding roller 38 (speed at which the sheet is fed from the ADU 5 to the intermediate feeding roller 38). The process speed is a speed at which a sheet is fed by both the intermediate feeding roller 38 and regist roller 37. Here, the drive of intermediate feeding roller 38 is controlled such that the feeding speed for duplex printing in the ADU 5 becomes 1 to 1.3 times the process speed.

Further, based on the information relating to the feeding speed acquired by the feeding speed information acquisition section 102, the drive controller 101 controls the drive of the intermediate feeding roller 38 with a feeding speed for sheet supply and a process speed. The feeding speed for sheet supply is a speed at which a sheet to be newly supplied to the intermediate feeding roller 38 is passed through the feeding roller 36 a (speed at which a sheet to be newly supplied is fed from the feeding roller 36 a to the intermediate feeding roller 38). The process speed is a speed at which a sheet is fed by both the intermediate feeding roller 38 and regist roller 37 at the time when a toner image is being formed onto the sheet. Here, the drive of intermediate feeding roller 38 is controlled such that the feeding speed for sheet supply becomes 1 to 1.3 times the process speed.

FIG. 4 is a timing chart showing sheet feeding timing at the time when duplex printing is performed for A4 size sheet and A3 size sheet. The upper half of FIG. 4 shows a timing chart in the case where five A4 size sheets are fed in a switchback manner (85 PPM (Print Per Minute)), and the lower half shows a timing chart in the case where five A3 size sheets are fed in a switchback manner (42 PPM). Further, in the timing charts of the respective sheet sizes, upper halves show the case where the one-side printed sheet is reversed before being discharged outside, and lower halves show the case where duplex printing is performed.

In the case of the duplex printing for A4 size sheets, images are formed in the order of: front (1) of first sheet, front (2) of second sheet, front (3) of third sheet, back <1> of first sheet, front (4) of fourth sheet, back <2> of second sheet, front (5) of fifth sheet, back <3> of third sheet, back <4> of fourth sheet, and back <5> of fifth sheet.

In the case of the duplex printing for A3 size sheets, images are formed in the order of: front (1) of first sheet, front (2) of second sheet, back <1> of first sheet, front (3) of third sheet, back <2> of second sheet, front (4) of fourth sheet, back <3> of third sheet, front (5) of fifth sheet, back <4> of fourth sheet, and back <5> of fifth sheet.

When the productivity at the duplex printing time is calculated based on the configuration and feeding speed of the image forming apparatus according to the embodiment, the following result is obtained. FIG. 5 is a view for explaining a sheet feeding path in the image forming apparatus according to the embodiment. Here, as an example, the sheet feeding speed and distance are set as shown in FIG. 5. In FIG. 5, LP represents process speed feeding distance in process speed area, Lr represents acceleration/reverse feeding distance (switchback distance) in acceleration/reverse area, and La represents duplex speed feeding distance in duplex feeding speed area.

In order to realize, at the duplex printing time, sheet feeding efficiency (duplex productivity 100%) equivalent to the case where one-side printed sheet is reversed before being discharged outside, the starting time of the drive of the regist roller 37 can be described as below and circulation time until the regist roller 37 is restarted for feeding a sheet to the ADU 5 can be represented by the following expression, in the case of, for example, 72 PPM or 85 PPM. Hereinafter, the duplex productivity means the sheet feeding efficiency at the time of duplex printing relative to the case where one-side printed sheet is reversed before being discharged outside, that is, indicates how the processing efficiency at the time of duplex printing is close to that at the time of one-side printing. TN5=60/PPM*5: circulation time

-   {4.16 sec (72 PPM), 3.53 sec (85 PPM)} -   Tat: duplex feeding total time [sec]     =Ta+Tp+Tr+Tra+Tr -   PPM: one side productivity (PPM for A4/LT size) 72, 85 PPM -   Vp: process speed [mm/sec] 340, (410 mm/sec) -   Vr: Reverse speed [mm/sec] 800 mm/sec Va: ADU feeding speed [mm/sec]     385 mm/sec, (465 mm/sec) -   Lp: process speed feeding distance [mm] about 367 mm -   Lr: acceleration/reverse feeding distance (switchback distance) [mm]     about 296 mm -   La: Duplex speed feeding distance [mm] about 692 mm -   Ta: Duplex speed feeding time [mm] 1797 sec, (1488 sec) -   Lpe: sheet length [mm] 216 mm (LT) -   Tpe: sheet reverse feeding time [sec] 0.369 sec -   Tp: process speed feeding time [sec] 1.079 sec, (0.895 sec) -   Ts: switchback time (reverse time) [sec] about 0.1 sec -   Tra: regist aligning time [sec] about 0.07 sec -   Tr: acceleration/reverse feeding time [sec] about 0.27 sec -   To: other required time (including loss at acceleration/deceleration     time and the like: 100 msec) about 0.10 sec     Note that numerical values in the parentheses represent feeding data     obtained in the case of 85 PPM.

It can be seen from the above that, in the case of a 72-PPM machine with a process speed of 340 mm/sec, duplex feeding total time Tat is 3.79 sec, which is smaller than 4.16 sec of circulation time TN5 of five sheets. Therefore, the processing for the five sheets satisfies the circulation condition, with the result that duplex productivity of 100% can be obtained. Similarly, in the case of an 85-PPM machine with a process speed of 410 mm/sec, duplex feeding total time Tat is 3.29 sec, which is smaller than 3.53 sec of circulation time TN5 of five sheets. Thus, in both above cases, high duplex productivity can be obtained.

In the present embodiment, the ratio between the process speed and duplex feeding speed is set at 1:1.13 and the CPU 108 changes only the rotation number of the motor to thereby realize two process speeds. As a result, the control that satisfies duplex productivity of 100% can be realized.

Further, when a setting that satisfies the above conditions in terms of the sheet feeding distance, sheet feeding speed, printing speed (PPM) is performed, duplex productivity of 100% can be realized.

In the case where there is a restriction from sheet interval at the time of sheet supply or reverse feeding speed, it is possible to cope with it by accelerating the feeding speed at the time of duplex printing and, further, factors such as the feeding speed, process speed, PPM, duplex feeding speed, reverse feeding distance are used to easily make a calculation selection.

In the present embodiment, the drive of the motor that drives the fixing section 24 is divided, and a clutch mechanism is used to turn ON/OFF the transfer of the drive force. In the case where one side printing is sequentially performed, the clutch is turned OFF so as not to drive the feeding rollers in the ADU 5. Further, a change in the ratio of the drive force divided from the motor for the fixing section 24 at the input time can realize speed change. In addition, a change in the drives of the feeding rollers 36 a to 36 d after the input can also realize a change in the sheet feeding roller.

The image forming apparatus according to the present embodiment employs alternating circulation mode of “one side-both sides-one side-both sides” to perform sheet feeding control at the time of duplex printing, so that it is only necessary for the reverse feeding section or duplex feeding section to perform sheet control for the printing section one time per two sheets. Therefore, the image forming apparatus does not use a pulse motor a lot for the drive of the feeding rollers in the ADU 5 but utilizes the clutch mechanism. Even in the case where the feeding rollers in the ADU 5 are driven by the clutch mechanism, if the intermediate feeding roller 38 is driven by, for example, a pulse motor, it is possible to realize a plurality of types of feeding speeds (for example, three feeding speeds of process speed, sheet supply speed (second speed), and duplex feeding speed (first speed)) by simply changing the drive frequency of the motor. Here, the intermediate feeding roller is constituted by a roller pair. Alternatively, however, it may be constituted by a plurality of roller pairs.

An example of the ratio of process speed: sheet supply speed: duplex feeding speed is shown below. 72 PPM mode 1:1.235:1.13 85 PPM mode 1:1.122:1.13

As described above, the drive controller 101 sets the sheet supply speed and duplex feeding speed to a speed higher than (1 to 1.3 times) the process speed, thereby reducing noise and stabilizing the sheet feeding control. That is, in the present embodiment, the ratio of the duplex feeding speed to the process speed is set at a predetermined value, i.e., 1:(1 to 1.3), and the ratio of the sheet supply speed to the process speed is set at a predetermined value, i.e., 1:(1 to 1.3).

The intermediate feeding roller 38 according to the embodiment can realize the following three sheet feeding speeds.

(1) Sheet supply speed 420 mm/sec

(2) Process speed 340 mm/sec

(3) Duplex feeding speed 385 mm/sec

That is, the sheet supply speed (first feeding speed) is higher than the process speed (second feeding speed), and the duplex feeding speed (third feeding speed) is also higher than the process speed. The duplex feeding speed is lower than the sheet supply speed.

The sheet supply speed is realized by a sheet supply unit (feeding rollers 36 a to 36 d), the process speed is realized by a process speed feeder (photoconductor drum and regist roller 37 that feed a sheet at a sheet feeding speed for toner image transfer), and the duplex feeding speed is realized by an automatic duplexing unit feeder (ADU 5).

As described above, by setting the sheet supply speed to a speed higher than the process speed, it is possible to shorten intervals between sheets to be sequentially fed and thereby to increase the number of sheets that can be fed in a given period time. Further, by setting the duplex feeding speed of the ADU 5 to a speed higher than the process speed, it is possible to realize high duplex productivity.

FIG. 6 is a timing chart showing drive timing of the regist roller 37, intermediate feeding roller 38, and feeding rollers other than the intermediate feeding roller 38 in the image forming apparatus according to the embodiment.

A sheet supplied from the cassette is fed by the intermediate feeding roller 38 to the regist roller 37 at a sheet supply speed of 420 mm/sec. The leading head of the sheet hits against a nip portion of the stopped regist roller 37, where aligning is performed. After that, the sheet is fed by the intermediate feeding roller 38 and regist roller 37 at a process speed of 340 mm/sec.

Subsequently, a succeeding sheet that has been temporarily put on standby for image forming onto one side thereof is fed by the intermediate feeding roller 38 to the regist roller 37 at a sheet supply speed of 420 mm/sec.

A case where image forming processing is performed for one side of the three sheets (in FIG. 6, timing chart relating to the first sheet is omitted) will be described. In order to form an image onto one side of a sheet, onto the other side of which an image has already been formed, the sheet is fed in a switchback manner. After the switchback, the sheet is fed in an accelerated manner to the portion in front of the ADU 5, where the feeding speed is slightly reduced to the ADU speed of 385 mm/sec, and the sheet is fed to the regist roller at that speed. It can be seen from FIG. 6 that at least three sheet feeding speeds are realized by the intermediate feeding roller 38.

In the sheet feeding timing chart shown in FIG. 6, a pre-regist SW serving as a sensor functions as a trigger for turning OFF the clutch. It is preferable to switch the pre-regist SW depending on the setting speed and stop time. This is because that there is a possibility that a sheet bends between rollers other than those for sheet feeding, which are disposed in the so-called an aligning section and perform skew correction and timing adjustment for the sheet.

The setting of the sheet feeding speed will next be described. In general, a clutch mechanism is used for the pick-up rollers for picking-up sheets from the cassettes 31 to 34. In such a case, the sheet feeding operation may get delayed more often than that performed by ordinary rollers. For example, a sheet feeding loss is generated due to delay of clutch connection time and a sheet feeding delay of the pick-up rollers 31 b to 34 b is generated. Such a delay in the sheet feeding time may cause jam or decrease in copy speed. In such a case, in order to ensure a margin for the sheet feeding delay and recover the sheet feeding relay, a setting may be made to make the sheet feeding speed and process speed at the time of printing an image different from each other in some cases.

However, it is not preferable to further increase the sheet feeding speed in an apparatus that feeds a sheet at high speed because friction noise between a sheet and guide at the sheet feeding time, drive noise, noise due to hitting of a sheet to a guide at the sheet feeding time, and the like are increased. Therefore, the sheet feeding speed is set in a range in which the sheet feeding operation can be stably performed.

The setting of the sheet feeding speed at the duplex feeding time (sheet feeding operation in the ADU 5) will next be described. The setting of the sheet feeding speed at the duplex feeding time is often made individually in each machine according to the machine type or printing speed (PPM). If a higher sheet feeding speed than is necessary is set, the temperatures of a drive motor and clutch are increased or it becomes difficult to perform stop control for a sheet. In the case where configuration that uses a pulse motor a lot is employed, although stable sheet feeding operation can be performed, manufacturing cost becomes increased.

In the case where two types of clutches are used to control the drive of the feeding roller on the upstream side relative to the intermediate feeding roller 38 (in the case where a dedicated motor for driving ADU feeding rollers is not provided, and the drive force for the ADU feeding rollers is transferred from fixing drive motor or the like), the sheet feeding speed realized by the feeding rollers needs to be made equal to the process speed or needs to be changed by a drive ratio. Also in this case, by allowing the sheet feeding speed realized by the intermediate feeding roller 38, process speed, and sheet feeding speed at the time of duplex printing to change in tandem with one another, stable sheet feeding operation can be realized.

When the sheet feeding speed in the ADU 5 is made equal to the sheet supply speed, the speed of the ADU 5 needs to be increased more than required, thereby increasing noise level at the sheet supply time. Therefore, the image forming apparatus according to the present embodiment is configured to reduce the noise by driving the respective speeds in an optimum manner.

In the present embodiment, only one pulse motor is used to drive the sheet feeding rollers disposed upstream of the regist roller to thereby realize the above three sheet feeding speeds, that is, the sheet supply speed required for feeding a sheet from the cassette; process speed for elongating the life of the photoconductor or consumable supply such as a development material; and duplex feeding speed for obtaining optimum sheet feeding speed of state productivity 100% (a state in which there is no difference in speed between one side printing and duplex printing, that is, at the time when the efficiency is maximum at the alternating circulation between them: except for the feeding time of the first and second sheets and the last two sheets after the completion of the duplex printing) with high duplex productivity.

The configuration obtained by adding only one pulse motor to the conventional configuration as described above satisfies three capabilities of stability in paper feeding operation, increase in the life of consumable supply (or increase in copy speed), and high duplex productivity required in the image forming apparatus. At the time of duplex printing, sheet feeding speed can freely be set without the need of setting unnecessary sheet feeding speed.

According to the present embodiment, when an apparatus having a different process speed is to be developed, it is possible to set a feeding speed for realizing duplex productivity of 100% without changing mechanical parts, and simply by changing the content of a ROM that controls the drive of the motor, an image forming apparatus of a different type can be designed. That is, it is possible to provide an image forming apparatus capable of suppressing occurrence of a problem which is based on a sheet feeding speed with a simple configuration without increasing cost and changing the process speed.

Further, by setting the sheet supply speed to a speed higher than the process speed, it is possible to shorten intervals between sheets to be sequentially fed and thereby to increase the number of sheets that can be fed in a given period time. Further, by setting the feeding speed (duplex feeding speed) of the ADU to a speed higher than the process speed, it is possible to realize satisfactory duplex productivity.

Further, the configuration of the image forming apparatus according to the present embodiment, in which a pulse motor is used to drive the intermediate feeding roller, eliminates the need to manufacture the apparatus provided with different PPMs and process speeds. Although the PPM is taken as an example of the printing speed in the present embodiment, the same applies to CPM (Copy Per Minute) used in copy processing.

In the case where the clutch mechanism is used for obtaining the sheet supply speed, there is a threshold limit around 500 rpm. Thus, there is a limitation in terms of reduction in intervals between sheets. However, when the clutch mechanism is used to drive the feeding rollers on the upstream of the intermediate feeding roller, it is possible to realize cost reduction in the entire apparatus.

While the present invention has been described in detail according to the specific embodiment, it will be apparent to those skilled in the art that variations and modifications are possible without deviating from the broad principles and spirit of the present invention.

As has been described in detail, according to the present invention, it is possible to provide an image forming apparatus capable of suppressing occurrence of a problem which is based on a sheet feeding speed without changing the process speed. 

1. An image forming apparatus comprising: a drive controller that controls the drive speed of an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; and a feeding speed information acquisition section that acquires information relating the feeding speed of the sheet to be fed to the intermediate feeding roller, wherein the drive controller controls the drive of the intermediate feeding roller with a feeding speed for duplex printing and a process speed based on the information relating to the feeding speed acquired by the feeding speed information acquisition section, the feeding speed for duplex printing being a speed at which a sheet, which is to be resupplied to the intermediate feeding roller for image forming onto the second surface thereof after it has been passed through the regist roller and a toner image has been formed onto the first surface thereof, is received by the intermediate feeding roller, and the process speed being a speed at which a sheet is fed by both the intermediate feeding roller and regist roller, and the drive controller controls the drive of the intermediate feeding roller such that the feeding speed for duplex printing becomes 1 to 1.3 times the process speed.
 2. An image forming apparatus comprising: a drive controller that controls the drive speed of an intermediate feeding roller that feeds a sheet to a regist roller that performs skew correction for the sheet; and a feeding speed information acquisition section that acquires information relating the feeding speed of the sheet to be fed to the intermediate feeding roller, wherein the drive controller controls the drive of the intermediate feeding roller with a feeding speed for sheet supply and a process speed, the feeding speed for sheet supply being a speed at which a sheet to be newly supplied to the intermediate feeding roller is received by the intermediate feeding roller, and the process speed being a speed at which a sheet is fed by both the intermediate feeding roller and regist roller, and the drive controller controls the drive of the intermediate feeding roller such that the feeding speed for sheet supply becomes 1 to 1.3 times the process speed.
 3. The image forming apparatus according to claim 1, wherein the intermediate feeding roller is driven by a pulse motor.
 4. The image forming apparatus according to claim 1, wherein the motive force for driving a feeding roller that supplies the intermediate feeding roller with a sheet is transferred by a clutch.
 5. An image forming apparatus comprising: a sheet supply unit that feeds a sheet that has been picked up from a sheet housing section along a sheet feeding path at a first feeding speed; a process speed feeder that feeds the sheet that has been fed to a process section by the sheet supply unit at a second feeding speed lower than the first feeding speed; and an automatic duplexing unit feeder that feeds the sheet that has been fed to an automatic duplexing unit by the process speed feeder at a third feeding speed lower than the second feeding speed, wherein the sheet that has been fed by the automatic duplexing unit feeder is fed again to the process section.
 6. The image forming apparatus according to claim 5, wherein the process section has a photoconductor and transfers a toner image formed on the photoconductor onto a sheet.
 7. The image forming apparatus according to claim 5, wherein the automatic duplexing unit feeder performs sheet feeding operation such that the third feeding speed becomes lower than the first feeding speed. 